The study of the differentiation of the plasma membrane in the cellular slime mold Dictyostelium discoideum will have two parts. The first is an analysis of the manner in which cyclic AMP, the extracellular signal molecule which mediates the social behavior of aggregating cells, is elaborated, stored, and released by signalling cells and how it is subsequently received, hydrolyzed and possibly reaccumulated. To accomplish this, intracellular and extracellular levels of cyclic AMP, membrane bound adenylate cyclase, phosphodiesterase, and cyclic AMP binding activity will be followed during development. Secondly, we shall examine cell surface specification during development of intercellular adhesion and morphogenesis. Interphase cells will be synchronized and the polypeptide components of their isolated plasma membrane examined as a function of time by gel electrophoresis. We hope to identify thereby macromolecules associated with behavioral competences, the temporal evoluation of which we have already defined quantitatively in this system. Isolation of the plasma membrane will also permit a more direct analysis of the molecules involved in the processing of c-AMP. In addition, antisera specific for cells at different stages of differentiation accurately characterized with respect to behavior will be used to identify and map topographic specialization of the cell surface - for example the accumulation of aggregation-specific groups at the poles of aggregating cells.